The present invention relates to a reflected light sensor for detecting the presence or absence of an object.
A light sensor for detecting the presence of an object is disclosed in German Patent No. 3,513,671 and corresponding U.S. Pat. No. 4,782,224. In this system, a distance limit or remote switching point of the light sensor can be varied by employing a rotatably mounted deflection mirror. That is, the mirror is arranged to pivot thereby changing the location of the focal point of a bundle of received light in a direction transverse to an optical axis on a photoelectric transducer arrangement. The photoelectric transducer arrangement is composed of two photoelectric elements whose output signals charge a differential amplifier. Hence, a signal corresponding to a difference between radiation energies incident on the two photoelectric elements is present at the output of the differential amplifier.
In order to distinguish between a first state where a sensed object is disposed between the remote switching point and the light sensor and a second state where a sensed object is disposed at a distance greater than the remote switching point, the output signal of the differential amplifier is fed to an evaluation circuit which evaluates its amplitude and sign. If the output signal is positive, for example, and reaches a response threshold provided in the evaluation circuit, the sensed object is disposed between the remote switching point and the light sensor. If, however, the signal becomes smaller than the response threshold, the sensed object is disposed at a distance greater than the remote switching point.
In a reflected light sensor disclosed in German Patent No. 2,924,685 and corresponding U.S. Pat. No. 4,282,430, a light source with a first optical axis and a light receiver with a second optical axis are each accommodated in a pivotal mount positioned between the first and second optical axes. This makes it possible to vary an angle which defines a remote switching point or distance limit. Here, the mounts are pivoted by means of a spindle drive, thus changing the angle at which the two axes of the optical systems intersect each other and consequently changing the remote switching point or distance limit.
The drawback in such a light sensor is that some of its optical and/or optoelectronic components are not fixed to a housing but must instead be displaceable in the housing and only then is it possible to adjust the location of the remote switching point. Such a structure requires a lot of equipment, is complicated to install and is not very stable. In addition, the electrical line arrangement must be designed to allow the necessary freedom of pivotal movement and the entire arrangement requires a lot of space.